1. Field of the Invention
The invention relates to oil field tools. More particularly, the invention relates to multiple line hydraulically operated tools and the refreshing of the hydraulic fluid thereof.
2. Prior Art
Downhole tools employing hydraulic control lines that have been deleteriously affected by contamination have been known for more than twenty years. Contamination of the hydraulic fluid can cause anything from a minor reduction in efficiency of the tool to a complete tool failure.
Common manifestations of contaminated hydraulic fluids include plugged control lines and adversely affected seal systems. To alleviate these occurrences, that many times necessitate premature workover, prior art remedies include flushing hydraulic fluid to the annulus of the well or to the tubing. While such flushing does introduce fresh hydraulic fluid, it is less than entirely effective in most situations because there is no way to be certain that all of the fluid has flushed. Moreover, the opening which allows the flushed fluid to run to the annulus or tubing can malfunction and allow contaminants into the control line thus allowing the remedy to become a source of the problem. Additionally, the flushed fluid is lost and no analysis can be undertaken on that fluid regarding type and possible source of contamination.
Other prior art systems simply attempt to build hydraulic tools capable of operating properly with contaminated fluid. While this can be considered to solve the problem it does so only when such a tool is actually successfully engineered so to do and at great expense.
Filtering systems have also been employed but with only marginal success. Some of the contaminants actually are caused by an incompatibility between the hydraulic fluid and the elastomeric compounds in the system. When this is a cause, merely filtering the fluid only solves part of the problem. A failure is still inevitable because of the degraded elastomers.
Thus, despite the efforts made in the prior art to alleviate the contamination problems experienced by hydraulically controlled downhole tools the oilfield industry still suffers from the need to perform early workovers and replace tools due to hydraulic control line contamination.